Battery pack and cordless tool using the same

ABSTRACT

A battery device is constituted by connecting such cell assemblies in parallel as each includes: a first cell group having a plurality of cells connected in series; a housing container for housing the first cell group; current detector housed in the container for detecting a current to flow through the first cell group; a switching element connected with the first cell group for turning ON/OFF the current to flow through the first cell group; and a controller for controlling the ON/OFF of the switching element in response to the output signal of the current detector.

TECHNICAL FIELD

The present invention relates to a battery device employing a stackablecell assembly technology (as will be abbreviated into the “SCAT”) and acordless electric tool using the battery device.

BACKGROUND ART

First of all, the concept of the SCAT proposed by us is explained withreference to FIGS. 1A-1D.

The cordless electric tool such as an electric driver, an electric drillor an impact tool is constituted to include a motor for generating arotating power by reducing the speed of the motor by a speed reducingmechanism and then transmitting the rotating power to a tip tool.

In FIG. 1A, numeral 20 designates a cordless electric tool, which isconstituted to include a body trunk portion 20A and a handle portion20B. A tool 30 is attached to the tip of the body trunk portion 20A. Thehandle portion 203 has its one end connected to the body trunk portion20A and mounts a battery device 10 at its other end portion.

All these cordless electric tools are determined by the makers in therated voltage (as will be abbreviated into “V”) and the current capacity(or the ampere time, as will be abbreviated into “Ah”). The ratedvoltage (V) is determined on the basis of both the magnitude of therotating power to be transmitted to the tool and the voltage necessaryfor driving the motor for generating the rotating power. On the otherhand, the current capacity (Ah) is determined by both the magnitude ofthe load current of the motor and the specifications of the time period,for which the tool can be continuously used. For example, the electrictool having the battery device of 3 Ah mounted thereon is characterizedto feed an electric current of 3 A continuously for one hour to themotor.

These rated voltage and current capacity are determined individually forevery tools by the makers so that their values cannot be arbitrarilychanged or modified by the users.

On the contrary, the SCAT proposes an electric tool of such a newconcept that the current capacity (Ah) can be arbitrarily selected bythe user although the rated voltage (V) of the electric tool isdetermined by the maker.

This new concept is desired in that one cordless electric tool cansatisfy the various needs of the user. When the electric tool is used ina narrow place such as the ceiling space, for example, the user willdesire the electric tool as light as possible better than the electrictool having a large current capacity. However, a half or so of theweight of the existing cordless electric tool is occupied by a batterypack or a battery device, and only the battery pack fitting the ratedvoltage and the current capacity of the electric tool can be mounted sothat the weight of the electric tool cannot be changed for anyoperation.

In case it is desired to continue an operation for a long time, on theother hand, the desired electric tool can be used without its batterypack being frequently charged. However, the electric tool of the priorart is prefixed in the current capacity so that it cannot use batterypacks of different current capacities for different operations.

The cordless electric tools of many kinds can naturally use tools ofdifferent situations for the different operations. However, the userwill not desire to prepare many electric tools and to bring them to theworking sites.

The SCAT can satisfy these various needs of the user. For example, thedifferences between the existing battery device and the battery deviceusing the SCAT are described for the case, in which the electric toolhas a rated voltage of 18 V and a current capacity of 3 Ah.

FIG. 1B shows the constitution of the battery device of the prior art ofthe case, in which a NiCd cell of a nominal voltage of 1.2 V is used asthe battery cell. This battery device is constituted by connectingfifteen cells C1 to C15 in series and housing them in a battery packcontainer 10A.

In case the lithium cells are used as the battery cell, on the otherhand, their nominal voltage is as high as 3.6 V, and the currentcapacity is so small as about 1.5 Ah. As shown in FIG. 1C, therefore,the battery device is constituted by connecting the series connection ofthe five cells C11 to C15 and the series connection of the five cellsC21 to C25 in parallel and by housing the totally ten battery cells inthe battery pack container 20A.

In the case of using the SCAT, on the contrary, the maker prepares thecell assembly, in which cells of the number needed for generating therated voltage of the cordless electric tool are stored, as shown in FIG.1D. In case the cell assembly is to be constituted by the lithium cells,for example, a cell assembly 100A is constituted by connecting fivebattery cells C11 to C15 having a nominal voltage of 3.6 V in series andby housing them in a container. Likewise, a cell assembly 100B isconstituted by connecting the battery cells C21 to C25 in series and byhousing them in the assembly container. These cell assemblies 100A,100B, - - - , and 100N are so constituted that they may be connected,when stacked, in parallel.

The user can use one cell assembly as a battery device of 1.5 Ah, andcan use two cell assemblies as a battery device of 3 Ah. In other words,the current capacity (Ah) of the cordless electric tool can beselectively determined by the user.

When the cell assembly is to be prepared by using the SCAT, it isdesired to use the lithium cells having a high nominal voltage and asmall current capacity. This is because the weight of the cell assemblycan be reduced and because the current capacity can be finely selectedby the user.

Here, the lithium cell indicates a vanadium-lithium cell, a manganeselithium cell or the like, which employs a lithium-aluminum alloy at itscathode and uses an organic electrolyte. On the other hand, the lithiumion cell generally employs cobaltous lithium in the anode and graphitein the cathode and uses an organic electrolyte as the electrolyte.Herein, for conveniences, the organic electrolyte secondary batteryincluding the lithium cell and the lithium ion cell will be generallyand merely called as the lithium cell.

As the prior art like the SCAT, there has already been proposed ordeveloped the battery device, which is so constituted in the mobileelectric device, e.g., a camera or a personal computer as ca connect aplurality of chargeable cells in parallel. For example, Patent Document1 discloses a battery pack, which is used in a camera or the like andwhich can mount a desired number of auxiliary cells in addition to themain cell. In the case of the cordless electric tool, however, thereexist technical problems of qualities different from those of the OAdevice or the mobile electronic device. Therefore, these problems haveto be solved in case the battery device for the electric tool isdeveloped by using the SCAT.

At first, one example of the cordless electric tool of the prior art isdescribed with reference to FIG. 2A and FIG. 2B.

FIG. 2A shows the appearance of the cordless electric tool of the priorart, and FIG. 2B shows the electric circuit of the electric toolschematically. The electric tool 20 such as an electric driver, anelectric drill or an electric wrench is constituted to include a bodytrunk portion 20A and a hand portion 20B connected to the body trunkportion 20A, and the battery device 10 is mounted on the end portion ofthe handle portion 20B.

In the housing of the body trunk portion 20A, there are housed a DCmotor 210 for generating a rotating power, and a speed reducingmechanism portion 202 for reducing the rotating speed of the DC motor201. A tip tool 30 such as a drill or a driver is attached to the tip ofthe speed reducing mechanism portion 202. In the case of the impacttool, an impact mechanism unit (although not shown) is interposedbetween the speed reducing mechanism portion 202 and the tip tool 30.Moreover, a trigger 203 is disposed near the connecting portion betweenbody trunk portion 20A and the handle portion 20B.

As shown in FIG. 2B, a trigger switch 203A, the motor 201 and aswitching element such as an FET are connected in series between the twoterminals of the battery device 10. To the gate of the switching element205, there is applied the pulse signal, which has its pulse widthmodulated by a control circuit 204. With this control circuit 204, thereis connected a variable resistor 203B, which has its resistance variedin association with the operation of the trigger switch 203A. The pulsewidth of the output pulse of the control circuit 204 is varied byvarying that resistance.

When the trigger 203 of FIG. 2A is pulled, the switch 203A of FIG. 2B isclosed to apply the driving voltage is applied to the motor 201 by thebattery device 10 only while the switching element 205 is ON, so thatthe motor 201 rotates. This rotating force is transmitted through thespeed reducing mechanism 202 to the tip tool 30.

When the trigger 203 is pulled more deeply, the resistance of thevariable resistor 203B varies. As a result, the pulse width of thepulses to be applied from the control circuit 204 to the gate of theswitching element 205 is enlarged. As a result, the ON period of theswitching element 205 is elongated to increase the average of the drivevoltage to be applied to the motor 201. Thus, the rotating speed of themotor 201 can be controlled according to the pulling stroke of thetrigger 203 thereby to control the magnitude of the rotating power to betransmitted to the tip tool 30. Moreover, the forward/backward rotatingdirection of the motor 201 can be switched by changing a switch 206connected with the two ends of the motor 201.

-   [Patent Document 1] JP-A-2001-229891

DISCLOSURE OF INVENTION

According to our investigations, it has been found that the followingtechnical problems arise when the battery device using theaforementioned SCAT is employed in the cordless electric tool thus fardescribed.

(1) Countermeasures Against Overcurrent

The battery device 10 of the cordless electric tool 20 is used as apower source for feeding the drive voltage of the motor 201, and themotor 201 is used to generate the rotating power to be transmitted tothe tool 30. The tip tool 30 is exemplified by a drill or a driver butis employed to work a workpiece so that the magnitude of a load to beapplied to the tool 30 is so largely fluctuated as could not occur in acamera or a personal computer. If the fluctuations of the load on thetool 30 are serious, the fluctuations of the loading current through themotor 201 are naturally so dangerous that an overcurrent may also flowinto the battery device 10.

Now, if the battery device 10 has a terminal voltage E, if the motor 201has a counter electromotive force E and if the motor 201 has an armatureresistance Ra, the current Ia to flow through the armature winding ofthe motor 201 is expressed by Ia=(V−E)/Ra. Therefore, the counterelectromotive force E instantaneously approaches 0 so that the currentIa abruptly rises to several 10 A, when the tip tool 30 bits theworkpiece so that the motor speed approaches 0.

In case cell assembles for generating voltages as high as 18 V or 24 Vare connected in parallel, an overcurrent may dangerously flow if thecharges of the cell assemblies are unbalanced. If a cell assembly havingfive battery cells fully charged and a cell assembly having five batterycells having a charge of 0% are connected in parallel, a current ofseveral 10 A may flow through the closed circuit of the two cellassemblies.

In case, however, a lithium cell having a current capacity of 1.5 Ah isused as the battery cell, the battery cell may be damaged, if a currentas high as about 30 A flows even for a short time period.

Likewise, in case the cell assembly having the fully charged batterycells and the cell assembly having the battery cells of a charge of 0%are connected in parallel and connected with the electric tool body, theload of the fluctuations of the load current of the motor may be appliedto one cell assembly thereby to damage the cell assembly itself.

In the battery device of the electric tool thus using the SCAT,countermeasures have to be taken against the overcurrent, which may beproduced for various causes. Especially in case the lithium cell isused, the countermeasures against the overcurrent are important becausethe current capacity (Ah) of the battery cell is smaller than that ofthe NiCd cell or the like.

(2) Selection of Assembly Suited for Characteristics of Electric Tool

The cordless electric tool is diversified into many kinds including anelectric driver, an electric drill, an electric circular saw and animpact driver, and has a wide range of load fluctuations in dependenceupon the tool kind. In the case of the electric drill, for example, theload current of the motor may become six or seven times as high as theordinary one, if the tip tool bites the workpiece. In the case of theimpact driver, on the other hand, the load fluctuations are relativelysmall so that the fluctuations of the load current of the motor are alsorelatively small. This phenomenon that the load fluctuations areremarkably different for the tool kinds is not found in the mobileelectronic device such as the camera or the OA device.

The maker of the battery device for the electric tool of the prior arthas determined the rated voltage and the current capacity of the batterypack while considering the differences in those load fluctuations.

However, the user of the battery device using the SCAT can select thevalue of the current capacity of the device, and may employ the cellassembly unfitted for the magnitude of the fluctuations of the loadcurrent of the electric tool. It is, therefore, important to guide theuser so that the user can select the cell assembly proper for the kindand characteristics of the electric tool. These technical problems areso specific to the electric tool that they are not found in otherelectronic devices such as the camera or the OA device.

(3) Countermeasures against Elongation of Charging Time

In the electronic device such as the camera or the personal computer, itis general that the cells are individually charged even in case they areconnected in parallel. In case, however, the battery device 10 to beused in the electric tool is to be charged with the charger, it is thecurrent practice that the cell packs are individually charged.Therefore, when the battery pack, in which fifteen NiCd battery cells ofnominal voltage of 1.2 V are housed, is charged, the fifteen cells arecharged all at once.

In the battery device prepared by the SCAT, on the contrary, the numberof battery cells to be housed in the cell assembly is smaller than thatof the prior art. This raises a problem that the charging time period islonger than that of the prior art if the charge is performed for eachcell assembly.

On the other hand, it is conceivable to charge cell assemblies of apredetermined number simultaneously. The user using the battery devicewith the SCAT can arbitrarily select the number of cell assemblies used.It is, therefore, inconvenient for the user that what can be selected isto charge only the cell assemblies of a predetermined number. In otherwords, it is desired for the user that cell assemblies of an arbitrarynumber can be charged all at once.

A main object of the invention is to provide a battery device using theSCAT and a cordless electric tool using the device, and a battery devicesolving the aforementioned technical problems and a cordless electrictool using the device.

Specifically, an object of the invention is to solve the aforementionedtechnical problem (1) and to provide a battery device and a cordlesselectric tool, which do not damage the battery cells and the cellassembly, even if the load current of the motor is drasticallyfluctuated by the load fluctuations of the electric tool, and in whichthe battery cells and the cell assemblies are not damaged even if thecell assemblies of different charges are connected in parallel.

In order to achieve the aforementioned objects, according to theinvention, there is provided a cell assembly characterized bycomprising: a first cell group having a plurality of cells connected inseries; a housing container for housing said first cell group; currentdetecting means housed in said container for detecting a current to flowthrough the first cell group; a switching element connected with saidfirst cell group for turning ON/OFF the current to flow through saidfirst cell group; and means for controlling the ON/OFF of said switchingelement in response to the output signal of said current detectingmeans.

Another characteristic of the invention is that each cell constitutingthe cell group uses a lithium cell.

Another characteristic of the invention is that the cell assemblycomprises: voltage detecting means for detecting the individual cellvoltages of said first cell group; and control means for controlling theON/OFF of said switching element in response to the output signal ofsaid voltage detecting means.

Another characteristic of the invention is that said housing containerhas a pair of first discharge terminals formed on its first face andconnected with the two terminals of said first cell group, and such apair of second discharge terminals formed on its second face confrontingsaid first face as are connected with the two terminals of said firstcell group.

Another characteristic of the invention is that said housing containerhas such a pair of charging terminals formed on its third face differentfrom said first face and said second face as are connected with the twoterminals of said first cell group.

According to another characteristic of the invention, there is provideda battery device characterized by comprising: a first cell group and asecond cell group each having a plurality of cells connected in series;a first container for housing the first cell group and a secondcontainer for housing the second cell group; first current detectingmeans for detecting a current to flow through said first cell group, andsecond current detecting means for detecting a current to flow throughsaid second cell group; a first switching element connected with saidfirst cell group for turning ON/OFF a current to flow through said firstcell group, and a second switching element connected with said secondcell group for turning ON/OFF a current to flow through said second cellgroup; first control means for controlling the ON/OFF of said firstswitching element with the output signal of said first current detectingmeans, and second control means for controlling the ON/OFF of saidsecond switching element with the output signal of said second currentdetecting means; first discharge terminals formed on the first faces ofsaid first and second housing containers and connected with the twoterminals of the individual cell groups; second discharge terminalsformed on such second faces as confronting the first faces of said firstand second housing containers, and connected with the individual cellgroups; and engagement members for connecting the first dischargeterminals formed on the first face of said first housing container andthe second discharge terminals formed on the second face of said secondhousing container.

According to another characteristic of the invention, there is provideda cordless electric tool characterized by comprising: a motor forgenerating a rotating power; a tool to be driven by said motor; and abattery device for feeding said motor with a DC voltage, and in thatsaid battery device has one or more cell assemblies each including: afirst cell group having a plurality of cells connected in series; ahousing container for housing said first cell group; current detectingmeans housed in said container for detecting the current to flow throughthe first cell group; a switching element connected with said first cellgroup for turning ON/OFF the current to flow through said first cellgroup; and means for controlling the ON/OFF of said switching element inresponse to the output signal of said current detecting means.

According to another characteristic of the invention, there is provideda cordless electric tool characterized by comprising: a tool bodyhousing a motor for generating a rotating power, and a speed reducingmechanism for reducing the speed of said rotating power; a handleportion connected to said tool body; and a battery device mounted at theend portion of said handle portion on the opposite side of saidconnected portion, and in that said battery device has one or more cellassemblies each including: a first cell group having a plurality ofcells connected in series; a housing container for housing said firstcell group; current detecting means housed in said container fordetecting the current to flow through the first cell group; a switchingelement connected with said first cell group for turning ON/OFF thecurrent to flow through said first cell group; and means for controllingthe ON/OFF of said switching element in response to the output signal ofsaid current detecting means.

According to another characteristic of the invention, there is provideda cordless electric tool characterized by comprising: a tool bodyhousing a motor for generating a rotating power, and a speed reducingmechanism for reducing the speed of said rotating power; a handleportion connected to said tool body; and a battery device mounted at theend portion of said handle portion on the opposite side of saidconnected portion, and in that said battery device includes: a firstcell group and a second cell group each having a plurality of cellsconnected in series; a first container for housing the first cell groupand a second container for housing the second cell group; first currentdetecting means for detecting a current to flow through said first cellgroup, and second current detecting means for detecting a current toflow through said second cell group; a first switching element connectedwith said first cell group for turning ON/OFF a current to flow throughsaid first cell group, and a second switching element connected withsaid second cell group for turning ON/OFF a current to flow through saidsecond cell group; first control means for controlling the ON/OFF ofsaid first switching element with the output signal of said firstcurrent detecting means, and second control means for controlling theON/OFF of said second switching element with the output signal of saidsecond current detecting means; first discharge terminals formed on thefirst faces of said first and second housing containers and connectedwith the two terminals of the individual cell groups; second dischargeterminals formed on such second faces as confronting the first faces ofsaid first and second housing containers, and connected with theindividual cell groups; and engagement members for connecting the firstdischarge terminals formed on the first face of said first housingcontainer and the second discharge terminals formed on the second faceof said second housing container.

The remaining characteristics of the invention are more clearlyunderstood from the description to be made in the following.

The following advantages are obtained according to the invention.

(1) Since cell assemblies of an arbitrary number can be mounted on anelectric tool, it is possible to provide a cordless electric tool, inwhich the user can select the current capacity (Ah).(2) Since the cell assemblies of an arbitrary number can be mounted onthe electric tool, the user can adjust the weight of the electric tool.(3) Since the cell assembly of the battery device mounted on theelectric tool has a switching element for interrupting the current whenthe current to flow through the cell group is at a predetermined rate orhigher, the cell group can be protected against an excessive current dueto load fluctuations or the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1D are explanatory views for explaining the concept of theinvention.

FIG. 2A is a schematic view of a cordless electric tool of the priorart.

FIG. 2B is an explanatory diagram of a motor current of the cordlesselectric tool of the prior art.

FIG. 3 is a circuit diagram showing one embodiment of a battery deviceaccording to the invention.

FIG. 4A is a sectional view showing one embodiment of a cell assemblyconstituting the battery device according to the invention.

FIG. 4B is a side elevation of the cell assemblies constituting thebattery device according to the invention.

FIG. 4C is a sectional view of a connecting portion of the cellassemblies constituting the battery device according to the invention.

FIG. 4D is an upper face view of the cell assemblies constituting thebattery device according to the invention.

FIG. 4E is a schematic view of the battery device, in which the cellassemblies according to the invention are stacked.

FIG. 5A is an electric circuit diagram at the time when the cordlesselectric tool according to the invention is connected with the batterydevice.

FIG. 5B is a sectional view of a cordless electric tool according to theinvention at the time when one cell assembly is mounted.

FIG. 5C is a sectional view of a cordless electric tool according to theinvention at the time when two cell assemblies are mounted.

FIG. 6A is a sectional view of a charging device for charging thebattery device according to the invention.

FIG. 6B is an electric circuit diagram of the charging device forcharging the battery device according to the invention.

FIG. 6C is a flow chart showing the control flow of the charging devicefor charging the battery device according to the invention.

BEST MODE FOR CARRYING OUT OF THE INVENTION

The invention will be described on its embodiments consecutively in theorder of (1) Constitution of Battery Device, (2) Constitution ofElectric Tool Body, and (3) Constitution of Charger.

(1) Constitution of Battery Device

(1.1) Circuit Constitution

Here is described a cell assembly constituting the battery deviceaccording to the invention. FIG. 3 shows an electric circuit diagram, inwhich cell assemblies 100A and 100B are connected in parallel. Theelectric circuit of the cell assembly 100A is identical to that of 100B,and the following description is made only on the electric circuit ofone cell assembly 100A.

In this embodiment, the cell assembly 100A includes five lithium cellsC11 to C15 connected in series. These cells C11 to C15 will be called acell group C10.

The cell group C10 has its positive terminal connected with adischarging positive terminal DC and its negative terminal connectedwith a common negative terminal C0 through a switching element 101. Thisswitching element 101 is composed of an FET 102 and a diode 103connected between the source and drain of the FET 102.

Numeral 104 designates an overcurrent detecting circuit, which isconnected between the source and drain of the switching FET 102 so thatit outputs a signal proportional to the magnitude of the current to flowbetween the source and the drain. The output signal of the overcurrentdetecting circuit 104 is applied through a diode 109 to the gate of theswitching FET 102 and is introduced into an overcurrent signal detectionterminal OC. The signal at this terminal OC is applied, if necessary, toa control circuit 204 (FIG. 2B) of the cordless electric tool and amicrocomputer 530 (FIG. 6B) of a charger 50.

On the other hand, the lithium cells C11 to C15 are connected withprotection circuits 105 and 106 for protecting the cells. Theseprotection circuits are exemplified by the IC (MM1414 or MM3090) ofMitsumi Denkisha. This protection IC is constituted to include fourinput terminals at the maximum and to generate an output signal when apredetermined or higher voltage enters any of the input terminals. Theoutput signals of the protection circuits 105 and 106 are introducedthrough diodes 110 and 111, respectively, into an overvoltage detectionterminal LE. The signal of this terminal LE is applied to themicrocomputer 530 (FIG. 6B) of the later-described charger 50. On theother hand, the output signals of the protection circuits 105 and 106are applied through diodes 107 and 108, respectively, to the gate of theswitching FET 102. A thermistor 113 for detecting the temperature of thecell group C10 is connected with the source or drain of the switchingelement 101. This temperature detection signal is guided to a signalterminal LS and is applied to the microcomputer 530 of thelater-described charger 50 (FIG. 6B).

On the other hand, a resistor 114 indicates the cell number of the cellgroup C10 and has a resistance made different according to the number ofcells. An electric signal according to the resistance of the resistor114 is guided by a cell number signal detection terminal ST and isapplied to the microcomputer 530 (FIG. 6B) of the later-describedcharger 50. Between the positive terminal of the cell group C10 and acharging terminal CH, there is connected a thermostat 112, which acts tostop the charge when the temperature of the cell assembly 100A exceeds apredetermined temperature.

When the cell assembly 100A and the cell assembly 100B thus constitutedare connected in parallel, as shown in FIG. 3, the voltage differencebetween the cell group C10 and the cell group C20 may become large, asin case one cell group C10 is fully charged whereas the other cell groupC20 is 0. In this case, the overcurrent may flow into the closed circuitincluding the cell groups C10 and C20 and switching elements 101A and101B. In case, moreover, the voltage between the terminals DC and CO isfed to a motor 201 shown in FIG. 2B, the overcurrent may flow into thecell assemblies 100A and 100B if the load of the motor 201 is high.

According to the battery device of the invention, however, when theovercurrent flows into the cell group C10, the voltage between thesource and drain of the switching element 101 increases. When thisvoltage exceeds a predetermine value, the overcurrent detecting circuit104 generates the output signal. This output signal is applied throughthe diode 109 to the gate of the switching FET 102 to interrupt the FET102. As a result, the overcurrent flows to the cell group C10 thereby toprevent the same from being damaged.

When any of the cells of the cell group C10 is charged to a voltageexceeding a predetermined value, the protection circuits 105 and 106also generate output signals to interrupt the FET 102. It is, therefore,possible to prevent the overcharge of the cells C11 to C15.

(1.2) Structure of Cell Assembly

Next, the structure of the cell assembly of the battery device of theinvention is described with reference to FIG. 4A to FIG. 4E. As shown inFIG. 4A, the cell housing container is constituted to include an upperplate 301, a lower plate 302 and two side plates 303 and 304. The fivelithium cells C11 to C15 are arranged in that container. The individualcells C11 to C15 are connected in series by terminal plates 30, and thecell C11 has its anode connected with a terminal 306 whereas the cellC15 has its cathode connected with a terminal 307. A circuit board 308is arranged in the space between the upper plate 301 and the cell groupsC10 to C15 and is supported by support members 309. The circuit elements101 to 111, as shown in FIG. 3, are mounted on the upper face of thecircuit board 308.

Adjacent to the side plate 303, on the other hand, there is arranged acharging terminal board 310, which is equipped thereon with positive andnegative charging terminals CH and CO and the signal detection terminalsLS, ST, LE and OC, as shown in FIG. 4B. In a portion of the side plate303 of FIG. 4A, there is formed an opening 303A, through which thevoltage can be applied to the terminals CH and CO.

The right side plate 304 of FIG. 4A is equipped with a first engagementmember 320A, which is made vertically movable for bringing the cellassembly 100A into engagement with the other cell assembly 100B(although not shown). The first engagement member 320A is equipped witha downward extending portion 327A, which is inserted into a hole portion328A. In this hole portion 32A, there is disposed a spring (althoughnot-shown) for pushing the first engagement member 320A upward intoengagement with a second engagement member 322A of another cell assemblyto be described hereinafter.

In FIG. 4A, one first engagement member 320A is shown, but another isdisposed on the deep side of the drawing. That is, the two firstengagement members 320A and 320B are provided, as shown in FIG. 4B.These first engagement members 320A and 320B are attached to a supportmember 323, as shown in FIG. 4C, which is provided with two uprightmetal plates 324A and 324B.

In the other cell assembly 100B, the second engagement members 322A and322B are attached to a support member 326, and metal plates 325A and325B are disposed in the engagement members 322A and 322B. When thesecond engagement members 322A and 322B are brought into engagement withthe first engagement members 320A and 320B, as shown in FIG. 4C, theother metal plates 324A and 324B are inserted into the metal plates 325Aand 325B so that the two cell assemblies 100A and 100B are connected toeach other.

As shown in FIG. 4A, the positive terminal 306 of the cell C11 isconnected through the wiring line on the circuit board 308 with themetal plates 324A and 325A, and the negative terminal 307 of the cellC15 is connected with the metal plates 324B and 32513 (FIG. 40).Likewise, the positive terminal (although not shown) of the cell C21 ofthe cell assembly 100B is connected with the metal plates 325A and 324A,and the negative terminal (although not shown) of a cell C25 isconnected with the metal plates 325B and 324B. As a result, when themetal plate 324A of the assembly 100A and the metal plate 325A of theassembly 100B are connected, and when the metal plate 324B of theassembly 100A and the metal plate 325B of the assembly 100B areconnected, the two cell assemblies 100A and 10013 are connected inparallel.

The first engagement members 320A and 320B, as urged upward by thesprings, are equipped with the metal plates 324A and 324B to act asdischarge terminals so that the metal plates 324A and 3248 are alwayspushed toward the metal plates 325A and 325B to act as the dischargeterminals of another cell assembly. Even if the cordless electric toolvibrates, it is possible to hold the contacts stable between the metalplates 324A and 325A and the metal plates 324B and 325B.

FIG. 4D shows the upper face view of the cell assembly 100A. On theupper face of the cell assembly container, there are arranged the firstengagement members, which are equipped with the discharge positiveterminal 324A connected with the positive terminal of the cell C11 andthe discharge negative terminal 324B connected with the negativeterminal of the cell C15. On the lower face opposed to that upper face,there are likewise arranged the second engagement members, which areequipped with the discharge positive terminal 325A and the dischargenegative terminal 325B.

On the other hand, the charging terminals of the cell group C10 isdisposed on the side face other than the upper and lower faces of thecontainer, so that the cell assemblies 100A and 100B can be chargedwhile being stacked and connected in parallel.

FIG. 4E shows a battery device 10, in which the two cell assemblies 100Aand 100B are stacked. In the upper face end portions of each of thebattery devices 100A and 100B, there are provided slide rails, which arecomposed of protrusions 331 and recesses 333. In the lower face endportions, there are provided slide rails, which are composed ofprotrusions 330 and recesses 334. The battery device 10, as composed oftwo cell assemblies 100A and 100B, is constituted by bringing the lowerslide rails of the cell assembly 100B into engagement with the upperrails of the cell assembly 100A.

(2) Constitution of Electric Tool Body

Next, the connection of the cordless electric tool and the batterydevice 10 according to the invention is described with reference to FIG.5A.

As described hereinbefore, the cordless electric tool according to theinvention allows the user to select its current capacity (Ah), but maydamage the battery device unless the tool employs the battery device ofa predetermined current capacity or higher. In the case of the driverdrill, for example, an excessive current may flow through the motor 201,when a tip tool 30 of FIG. 2B bits a workpiece, thereby to damage thebattery seriously if the current capacity (Ah) of the battery device 10is small. Therefore, the tool body of the invention is equipped with acontrol circuit for leaving the tool inactive in case a battery having asmaller current capacity than that necessary for the tool.

The embodiment, as shown in FIG. 5A, shows an example, in which thebattery device 10 including the three cell assemblies 100A, 100B and100C is mounted on an electric tool body 20. A motor 250 and a switchingFET 22 are connected in series between the discharging positive terminalDC and the negative terminal CO of the battery device 10. Moreover, thepositive terminal DC is connected through a trigger switch 251 and aresistor 262 with the gate of the switching FET 252 and the collector ofa transistor 253. The source of the FET 252 and the emitter of thetransistor 253 are commonly connected and are earthed to the ground.Moreover, the base of the transistor 253 is connected with the outputterminal of a control circuit 261.

Numeral 254 designates a constant-voltage power source, which isconstituted to include a regulator 256 and capacitors 255 and 257. Thisconstant-voltage power source 254 has its output voltage V0 fed to thecontrol circuit 261.

With the cell assemblies 100A, 100B and 100C, on the other hand, thereare respectively connected resistors 114A, 114B and 114C fordiscriminating cell numbers, as shown in FIG. 3. These resistors 114have resistances made different according to the number of cellsconstituting the cell assembly 100. If these resistances are detected,therefore, it is possible to discriminate the number of cells composingthe cell assembly 100. In this embodiment, it is assumed for the cellnumber of five that the resistors 114A, 114B and 114C have a value R1.

The cell assembly 100C has its detection terminal ST1 connected with thedetection terminal ST2 of the cell assembly 100B, and the cell assembly100B has its detection terminals ST1 and ST2 connected with the outputterminals ST2 and ST3 of the cell assembly 100A, respectively.

As a result, the detection terminals ST1, ST2 and ST3 of the cellassembly 100A are connected with the cell number discriminationresistors 114A, 114B and 114C, respectively. The detection terminalsST1, ST2 and ST3 of the cell assembly 100A are connected through pull-upresistors 258, 259 and 260, respectively, with the power source voltageterminal D of the control circuit 261 and with input terminals A, B andC. If the pull-up resistors 258, 259 and 260 individually have a valueR2, if the constant-voltage power source 254 has an output voltage V0and if the cell number discrimination resistor 114 has a resistance R1,a voltage of R1/(R1+R2)V0 is applied to the individual terminals A, Band C. In case the cell assembly is not connected, moreover, the voltageV0 is applied to the terminals A, B and C.

Now, if the R1 is 100Ω, if the R2 is 10 KΩ and if the V0 is 5 V, avoltage near 0 V is applied to the input terminals (A, B, C), in casethe cell assembly 100 is connected, and a voltage near 5 V is applied tothe input terminals (A, B, C), in case the cell assembly 100 is notconnected. If, therefore, the voltages to be applied to the terminals A,B and C are binarized with an intermediate threshold value between 5 Vand 0 V, the number of cell assemblies connected can be obtained as abinary signal. If the high level is 1 (high) and if the low level is 0(low), for example, the control circuit 261 can recognize that one cellassembly is connected when the terminals (A, B, C) are (0, 1, 1), thattwo cell assemblies are connected when the terminals (A, B, C) are (0,0, 1), and that three cell assemblies are connected when the terminals(A, B, C) are (0, 0, 0). The control circuit 261 is constituted inadvance to generate an output signal at an output terminal E inaccordance with the values (A, B, C). For example, it is preset that theoutput terminal E is 0 (low) when (A, B, C) are (0, 0, 0) and (0, 0, 1),and that the output terminal E is 1 (high) when (A, B, C) are (0, 1, 1)and (1, 1, 1).

The actions of the circuit shown in FIG. 5A are described in thefollowing. When the user turns ON the trigger switch 251, the positivevoltage of the battery device 10 is applied through the switch 251 andthe resistor 262 to the gate of the switching FET 252 so that the FET252 is turned ON.

On the other hand, the control circuit 261 detects the number ofconnected cell assemblies 100 with the magnitudes of the signals toenter the input terminals A, B and C. In case the cell assemblies 100 ofthe necessary number are not connected with the tool 20, the signal at 1is outputted from the output terminal E. With this signal, thetransistor 253 is turned ON. As a result, the gate and source of theswitching FET 252 are shorted so that the FET 252 is turned OFF. Inother words, the tool 20 is controlled to become inactive, in case thecell assemblies of a number less than the preset value are connectedwith the control circuit 261.

FIG. 5B is a sectional view of the electric tool 20 according to theinvention. The motor 250, a speed reducing mechanism 202 and so on arehoused in a body trunk portion 20A, and the battery device 10 is mountedon one end of a handle portion 20B. On the other hand, FIG. 5C shows anexample, in which the two cell assemblies 100A and 100B are mounted asthe battery device 10.

(3) Constitution of Charger

Next, the constitution of the charger according to the invention isdescribed with reference to FIG. 6A and FIG. 6B. The charger 50 isconstituted to include a body 500 and a cell housing unit 501. The cellhousing unit 501 is so constituted as to house a plurality of cellassemblies 100. This embodiment presents an example for housing the twocell assemblies 100A and 100B, and is so designed as to house two ormore arbitrary cell assemblies.

On the bottom face 502 of the cell housing unit 501, there are mountedterminal plates 503A and 503B. Each of these terminal plates 503A and503B is equipped with terminals to be connected with the chargingpositive terminal CH, the charging negative terminal CO, and the signalterminals LS, ST, LE and OC, as shown in FIG. 4B.

FIG. 6B shows an electric circuit of the charger 50. The voltage of acommercial AC power source 60 is converted into a DC voltage by arectifying smoothing circuit 510, and is then applied through aswitching element 511 to a transformer 512. By controlling the ON-timeof the switching element 511, the average value of the voltage to appearat the secondary side winding of the transformer 512 can be controlledin its magnitude.

The voltage of the secondary side winding of the transformer 512 isconverted again into a DC voltage by a rectifying smoothing circuit 513,and is then applied to the charging positive terminal CH and thenegative terminal CO of the cell assemblies 100A and 100B thereby tocharge the cell groups C10 and C20 in those cell assemblies 100A and100B.

The magnitude of the charging current, which corresponds to the sum ofthe charging current of the cell assembly 100A and the charging currentof the cell assembly 100B, is detected by a charging current detectingcircuit 514 connected with the secondary side of the transformer 512,and is applied to the microcomputer 530.

On the other hand, the terminal voltages of the cell groups C10 and C20of cell assemblies 100A and 100B are detected by a cell voltagedetecting circuit 515, and are applied to the microcomputer 530.

Moreover, the signals indicating the temperatures of the cell groups C10and C20 of the cell assemblies 100A and 100B are applied from theterminal LS to the cell temperature detecting circuit, the output ofwhich is applied to the microcomputer 530. An overvoltage detectionsignal is applied, when it appears at the signal terminal LE, to themicrocomputer 530 and to a charge stopping circuit 520. This chargestopping circuit 520 sends, when the overvoltage detection signal comes,the output signal to a switching control circuit 531 thereby to turn OFFthe switching element 511.

A constant power source voltage Vcc, as generated by an auxiliary powersource circuit 525, is applied to the microcomputer 530. On the basis ofthe various detection signals, moreover, signals for instructing the setvoltage and the set current are sent to a current/voltage settingcircuit 518. A constant-current control circuit 516 compares the setvoltage of the setting circuit 518 and the charging current from thecharging current detecting circuit 514, and controls the ON/OFF of theswitching element 511 so that the charging current may be equal to theset current. Likewise, a constant-voltage control circuit 517 comparesthe set voltage of the setting circuit 518 and the cell voltage from thecell voltage detecting circuit 515, and controls the ON/OFF of theswitching element 511 so that the cell voltage may be equal to the setvoltage.

Moreover, the microcomputer 530 sends a signal to a display circuit 526thereby to display the charging action, and sends a signal to a fanmotor driving circuit 521 thereby to drive a fan motor 522. Themicrocomputer 530 controls a signal to a buzzer driving circuit 523thereby to sound a necessary buzzer 524.

Next, a control flow of the aforementioned charger is described withreference to FIG. 6C.

At Step S101, it is decided whether or not the cell assemblies 100A and100B have been set in the charger 50. If set, the number of cellassemblies connected with the charger 50 is detected at Step S102. Thereare many detecting methods, by which it is decided that the number ofcell assemblies is two, if signals enter a detection circuit 519 fromthe two LS terminals, and that the number is one, if the signal goesfrom one LS terminal.

At Step S103, a charging current Icrg is set according to the number ofcell assemblies 100 connected. The charging current Icrg is set to I1,if the number of cell assemblies 100 connected is one, and the chargingcurrent Icrg is set to I2, if two. Usually, the value I2 is set to twotimes as high as the value I1. At Step S104, moreover, the charge endingcurrent at the end of the charge is set. In case a nickel-cadmium cellor a nickel-hydrogen cell is to be charged, the cell voltage or the celltemperature is generally detected to decide the timing, at which thecharge is ended. In case a lithium cell is to be charged, the chargingcurrent is detected to decide the charge ending timing.

At Step S105, the charging voltage is set. For example, the chargingvoltage is set to VI, if the voltage of the cell assembly 100 is 18 V,and to V2, if the 14.4 V.

Next, at Step S106, the charge is started, and a constant-currentcontrol is made (at Step S107). In short, the control is made such thatthe current Iout to flow through the cell assembly 100 may be a constantcurrent value Icrg. At Step S108, it is decided whether or not acharging voltage Vout of the cell assembly 100 reaches a preset chargingvoltage Vcrg. In case the decision result is YES, the control isswitched to the constant-voltage control at Step S109. Specifically, theconstant-current control is made at first, in case the lithium cell ischarged, and the constant-voltage control is made after charged to apredetermined voltage. After switched to the constant-voltage control,the charging current Iout of the cell assembly 100 gradually drops. Itis decided (at Step S110) whether or not a preset charge ending currentIst has been reached. If the decision result is YES, the charge isended.

In the charging device of the invention, as has been describedhereinbefore, the different charging currents and charge ending currentsare set according to the number of cell assemblies to be connected.

The embodiments of the invention thus far described can be easilymodified in various manners without any change in the basic concept ofthe invention, and these modifications belong to the invention. Forexample, the overcurrent detecting circuit 104 in FIG. 3 is constitutedto detect the source-drain voltage of the switching FET 102, but mayalso be constituted such that a fixed resistor is connected in serieswith the cell group C10 and that the voltage between the two ends of thefixed resistor is detected. Moreover, the switching FET 102 has to bedisposed for each cell group, but may be disposed outside of the cellcontainer.

1-13. (canceled)
 14. An electric device configured to be connectable toa first battery pack including plural battery cells, a positive terminaland a negative terminal, and connectable to a second battery packincluding plural battery cells, a positive terminal and a negativeterminal, the electric device comprising: a first positive terminalconfigured to be connected to the positive terminal of the first batterypack; a first negative terminal configured to be connected to thenegative terminal of the first battery pack; a second positive terminalconfigured to be connected to the positive terminal of the secondbattery pack; a second negative terminal configured to be connected tothe negative terminal of the second battery pack; a first control signalterminal configured to receive one of a signal indicative of the numberof the plural battery cells of the first battery pack and a signalsupplied from a first protection circuit for protecting the pluralbattery cells of the first battery pack; a second control signalterminal configured to receive one of a signal indicative of the numberof the plural battery cells of the second battery pack and a signalsupplied from a second protection circuit for protecting the pluralbattery cells of the second battery pack; a switching element connectedto a current path between the first and second positive terminals andthe first and second negative terminals; and a controller configured tocontrol the switching element to be turned off based on the signal inputto one of the first and second control signal terminal.
 15. The electricdevice according to claim 14, wherein the plural battery cells of thefirst and second battery packs are lithium cells.
 16. The electricdevice according to claim 14, wherein the electric device includes oneof a cordless electric tool and a battery charger.
 17. The systemaccording to claim 14, wherein when the first battery pack and thesecond battery pack are housed in the cell housing unit, the firstbattery pack is connected to the second battery pack in parallel.
 18. Asystem comprising: a first battery pack including plural battery cells,a positive terminal and a negative terminal; a second battery packincluding plural battery cells, a positive terminal and a negativeterminal; and an electric device configured to be connectable to thefirst and second battery packs, the electric device including: a firstpositive terminal configured to be connected to the positive terminal ofthe first battery pack; a first negative terminal configured to beconnected to the negative terminal of the first battery pack; a secondpositive terminal configured to be connected to the positive terminal ofthe second battery pack; a second negative terminal configured to beconnected to the negative terminal of the second battery pack; a firstcontrol signal terminal configured to receive one of a signal indicativeof the number of the plural battery cells of the first battery pack anda signal supplied from a first protection circuit for protecting theplural battery cells of the first battery pack; a second control signalterminal configured to receive one of a signal indicative of the numberof the plural battery cells of the second battery pack and a signalsupplied from a second protection circuit for protecting the pluralbattery cells of the second battery pack; a switching element connectedto a current path between the first and second positive terminals andthe first and second negative terminals; and a controller configured tocontrol the switching element to be turned off based on the signal inputto one of the first and second control signal terminal.
 19. The systemaccording to claim 18, wherein the plural battery cells of the first andsecond battery packs are lithium cells.
 20. The system according toclaim 18, wherein the electric device includes one of a cordlesselectric tool and a battery charger.
 21. The system according to claim18, wherein when the first battery pack and the second battery pack arehoused in the cell housing unit, the first battery pack is connected tothe second battery pack in parallel.
 22. A system comprising: a firstbattery pack including at lease one battery cell, and a first protectioncircuit configured to protect the battery cell; a second battery packincluding at least one battery cell, and a second protection circuitconfigured to protect the battery cell; and an electric deviceconfigured to be connectable to the first and second battery packs, theelectric device including: a cell housing unit configured to house thefirst battery pack and the second battery pack; a first terminalconfigured to be electrically connected to the first battery pack, thefirst terminal being provided at the cell housing unit; a secondterminal configured to be electrically connected to the first protectioncircuit, the second terminal being provided at the cell housing unit; athird terminal configured to be electrically connected to the secondbattery pack, the third terminal being provided at the cell housingunit; a fourth terminal configured to be electrically connected to thesecond protection circuit, the fourth terminal being provided at thecell housing unit; a switching element configured to control a currentflowing through the first terminal and the third terminal; and acontroller configured to control the switching element based on signalsreceived by one of the second terminal and the fourth terminal.
 23. Thesystem according to claim 22, wherein the cell housing unit includes afirst housing part configured to house the first battery pack, and asecond housing part configured to house the second battery pack, thefirst terminal and the second terminal are provided at the first housingpart, and the third terminal and the fourth terminal are provided at thesecond housing part.
 24. The system according to claim 22, wherein whenthe first battery pack and the second battery pack are housed in thecell housing unit, the first battery pack is connected to the secondbattery pack in parallel.
 25. The electric device according to claim 22,wherein the battery cell of the first and second battery packs is alithium cell.
 26. The electric device according to claim 22, wherein theelectric device includes one of a cordless electric tool and a batterycharger.